This invention relates generally to the processing of a substrate utilizing a plasma in the production of integrated circuits, and specifically relates to the improvement of plasma processing involving a plasma etch.
Gas plasmas are widely used in a variety of integrated circuit fabrication processes, including plasma etching and plasma deposition applications. Generally, plasmas are produced within a process chamber by introducing a low-pressure process gas into the chamber and then directing electrical energy into the chamber for creating an electrical field therein. The electrical field creates an electron flow within the chamber which ionizes individual gas molecules by transferring kinetic energy through individual electron-gas molecule collisions. The electrons are accelerated within the electric field, producing efficient ionization of the gas molecules. The ionized particles of the gas and free electrons collectively form what is referred to as a gas plasma.
Gas plasmas are useful in a variety of different integrated circuit fabrication processes. One commonly used plasma process is a plasma etch process wherein a layer of material is removed or xe2x80x9cetchedxe2x80x9d from a surface of a substrate. The ionized gas particles of the plasma are generally positively charged. Within an etching process, the substrate is negatively biased such that the positive ionized plasma particles are attracted to the substrate surface to bombard the surface and thereby etch the substrate surface. For example, a substrate might be etched to remove an undesired layer of material therefrom prior to the deposition of a desirable material layer or coating on the substrate. Such a pre-deposition etch process is often referred to as etch cleaning of the substrate.
Generally, there are various different ways of producing a plasma within a process chamber. For example, a pair of opposing electrodes might be oriented within the chamber to capacitatively couple electrical energy to the plasma. A microwave resonant chamber utilizing ultra-high frequency microwave fields might also be utilized. Electron cyclotron resonance (ECR) devices, on the other hand, use controlled magnetic fields to induce circular electron flow within a process gas to create and sustain a plasma. Inductive coupling processes are also popular, and are particularly desirable for their capability of producing a high-density plasma. Inductively coupled plasmas (ICP""s) generally utilize a shaped coil or antenna positioned with respect to the process chamber to inductively couple energy into the chamber and thus create and sustain a plasma.
Various prior art processing systems have been utilized for the plasma processing of a substrate, such as plasma etching a substrate to clean a surface thereof. Despite the suitability of such systems for plasma etching and other plasma processing, these prior art systems have certain drawbacks associated therewith.
For example, conventional plasma processing systems often have very complicated designs which are not only difficult and expensive to manufacture and assemble, but the systems are also difficult and expensive to maintain. For example, plasma processing systems utilize numerous subsystems which must be integrated together with a process chamber. Plasma processing systems utilize electrical energy sources for biasing a substrate. Those electrical energy sources are operably coupled to a substrate support within the process chamber through appropriate lines or cables. Furthermore, the system might utilize heating and/or cooling assemblies for heating or cooling the substrate while it is being processed. Still further, various clamping structures are utilized for maintaining the substrate on a support during processing, and lift structures are utilized for lifting the substrate after it has been processed so that the substrate may be transferred out of the processing system and into another processing system or module. Gas may be provided to the back side of a substrate mounted on a substrate support to enhance the heating of the substrate during processing.
As may be appreciated, the various electrical, thermal, gas, and mechanical sub-systems must be integrated or coupled with a substrate support within a process chamber. Current systems have complicated designs which are difficult and expensive to manufacture and maintain. The complexity of such systems often requires that the system be shut down for one or more days while it is repaired or certain components are replaced. The disassembly and reassembly of the components is tedious. Furthermore, such a lengthy shutdown decreases the efficiency of the overall plasma processing system, thus further increasing the costs of maintaining and operating such a system.
With respect to another aspect of conventional systems, the design of the substrate support utilized therein often exposes high voltage and high frequency electrical lines and connections to the plasma created within the process chamber. The exposed lines and connections, which are coupled to high frequency or high voltage electrical sources utilized to bias the substrate, may cause arcing and shorting within the plasma, and other plasma instabilities. Such plasma instabilities detrimentally affect the overall plasma process.
An additional drawback within conventional plasma processing systems is that such systems often do not efficiently heat the substrate being processed. The substrate support on which the substrate rests in the process chamber is usually made predominantly of metal and is coupled to other metal structures and components within the processing system. The thermal conduction properties of the metal support leads to significant conductive heat loss from the substrate support to the attached structures and components and thereby inefficient conductive heating of the substrate on the support. While backside gas has been utilized in the past to provide better heat conduction between the metal substrate support and the substrate, such backside gas is not always sufficient to overcome the heat loss characteristics of the overall substrate support and attached components. Furthermore, the inefficient heat transfer characteristics of existing process system substrate supports makes precise heating of the substrate difficult.
Still another undesirable characteristic of conventional plasma processing systems is that non-uniformity within the plasma often creates etching of the substrate. As a result, a substrate surface may be nonuniformly etched due to plasma discrepancies over the surface of the substrate. For example, the plasma is often more dense in the center of the process space and proximate the center of the substrate than proximate the outer edges of the substrate. Therefore, a greater etch rate may occur proximate the center of the substrate.
Accordingly, it is an objective of the present invention to improve upon conventional plasma processing systems, and specifically to improve upon plasma etching systems to provide a more uniform etch of a substrate.
It is another objective of the present invention to increase the operational efficiency of a system by reducing the complexities of the system and reducing the cost of repairing and maintaining the system.
It is further an objective of the invention to utilize a system which may be readily and efficiently maintained.
It is still another objective of the invention to improve the heating characteristics of a plasma process system for efficient, uniform heating of a substrate.
These objectives, and additional objectives will become more readily apparent from the description of the invention below.
The present invention addresses the above objectives and provides a processing system which may be readily and inexpensively maintained while providing efficient plasma processing, such as plasma etching, of the substrate. The system uniformly and efficiently heats a substrate and provides variable DC voltage profiling across a substrate to provide a uniform etch.
To that end, the processing system of the invention comprises a process chamber having a top, bottom, and a side wall which defines a process space therein. The process chamber has an opening in the side wall to provide access to the process space. A substrate support assembly comprising a hollow plenum and a platen extends into the process space through the side wall opening. The substrate support assembly seals the side wall opening and supports a substrate horizontally within the process chamber opposite a plasma-generating assembly that is coupled to the process chamber. The hollow plenum has a conduit formed therein through which external sub-systems, such as gas supplies, RF and DC power supplies, and a cooling water supply may be coupled to the platen. In that way, all sub-system connections to the platen are maintained within the plenum conduit which is isolated from the process chamber. The substrate support assembly, including the plenum and platen, may be readily removed from the process chamber for repair and/or replacement. The platen may be quickly and readily removed from the plenum and replaced as necessary by disconnecting the external sub-systems within the plenum conduit from the platen. In that way, the time for repair and/or replacement of the substrate support assembly is significantly reduced.
The platen is formed of a ceramic material and has a resistance heater and electrical grid embedded therein. The resistance heater is operated to provide the desired heating of a substrate for plasma processing. A metal tube having a low thermal conductivity and a significantly smaller diameter than the platen is coupled to the platen and to a mounting flange which is mounted to the plenum. The tube limits conductive heat loss from the platen to the flange and plenum, and thus provides more efficient and uniform heating of a substrate on the platen surface. A backside heating gas is pumped through the conduit of the plenum and through the small diameter tube to an opening within the platen to introduce a backside heating gas to a substrate on the platen. The various sub-systems of the plasma processing system are all coupled to the platen through the plenum conduit and tube and thus are isolated from the plasma processing environment. Such isolation increases the overall life span of the components, including the power supply components and significantly reduces shorting or arcing within the plasma caused by exposed power supply components.
The grid embedded within the platen is coupled to a DC power supply and to an RF power supply simultaneously. The grid comprises two poles which are biased with both the DC power supply and RF power supply. The poles are electrically isolated and the DC bias supply creates a stable DC bias between the poles which is effective to electrostatically secure or clamp a substrate to the platen. The RF power supply has a variable output and creates an RF-induced DC bias on the electrically isolated poles of the grid. The variable RF power supply is operable to create different RF-induced DC biasing between the electrically isolated poles of the grid. In that way, a variable DC voltage profile is created across the substrate which is clamped to the platen. By varying the DC voltage profile across the substrate, in accordance with the principles of the present invention, non-uniformities within the plasma may be addressed. For example, the invention may be utilized to increase the etch rate at the periphery of the substrate to offset the generally higher etch rate at the center of the substrate caused by nonuniformities within the plasma density.
In one embodiment of the invention, the poles of the electrical grid are in the form of a center disk and an outer ring concentrically aligned with the disk. Other pole shapes might also be utilized for the platen grid to create the desired DC voltage profile across the substrate being processed. Further details regarding the invention are set forth in the Detailed Description hereinbelow.